Background: Cohort studies have suggested that nasal continuous positive airway pressure (CPAP) starting in the immediate postnatal period before the onset of respiratory disease (prophylactic CPAP) may be beneficial in reducing the need for intubation and intermittent positive pressure ventilation (IPPV), and in preventing bronchopulmonary dysplasia (BPD), in preterm or low birth weight infants., Objectives: To determine if prophylactic nasal CPAP (started within the first 15 minutes) or very early nasal CPAP regardless of respiratory status (started within the first hour of life), reduces the use of mechanical ventilation and the incidence of bronchopulmonary dysplasia without any adverse effects in preterm infants., Search Methods: A comprehensive search was run on 6 November 2020 in the Cochrane Central Register of Controlled Trials (CENTRAL via CRS Web) and MEDLINE via Ovid. We also searched the reference lists of retrieved studies., Selection Criteria: We included all randomised controlled trials (RCTs) and quasi-RCTs in preterm infants (under 37 weeks of gestation). We included trials if they compared prophylactic nasal CPAP (started within the first 15 minutes) or very early nasal CPAP (started within the first hour of life) in infants with minimal signs of respiratory distress with 'supportive care', such as supplemental oxygen therapy, standard nasal cannula, or mechanical ventilation. We excluded studies where prophylactic CPAP was compared with CPAP along with co-interventions., Data Collection and Analysis: We used the standard methods of Cochrane Neonatal, including independent study selection, assessment of trial quality, and extraction of data by two review authors., Main Results: We included eight trials (seven from the previous version of the review and one new study), recruiting 3201 babies, in the meta-analysis. Four trials, involving 765 babies, compared CPAP with supportive care, and three trials (2364 babies) compared CPAP with mechanical ventilation. One trial (72 babies) compared prophylactic CPAP with very early CPAP. Apart from a lack of blinding of the intervention, we judged seven studies to have a low risk of bias. However, one study had a high risk of selection bias. Prophylactic or very early CPAP compared to supportive care There may be a reduction in failed treatment (risk ratio (RR) 0.6, 95% confidence interval (CI) 0.49 to 0.74; risk difference (RD) -0.16, 95% CI -0.34 to 0.02; 4 studies, 765 infants; very low certainty evidence). CPAP possibly reduces BPD at 36 weeks (RR 0.76, 95% CI 0.51 to 1.14; 3 studies, 683 infants, moderate certainty evidence); there may be little or no difference in death (RR 1.04, 95% CI 0.56 to 1.93; 4 studies, 765 infants; moderate certainty evidence). Prophylactic CPAP may reduce the composite outcome of death or BPD (RR 0.69, 95% CI 0.40 to 1.19; 1 study, 256 infants; low certainty evidence). There may be no difference in pulmonary air leak (pneumothorax) (RR 0.75, 95% CI 0.35 to 1.16; 3 studies, 568 infants; low certainty evidence), or intraventricular haemorrhage (IVH) Grade 3 or 4 (RR 0.96, 95% CI 0.39 to 2.37; 2 studies, 486 infants; moderate certainty evidence). Neurodevelopmental impairment was not reported in any of the studies. Prophylactic or very early CPAP compared to mechanical ventilation There was probably a reduction in the incidence of BPD at 36 weeks (RR 0.89, 95% CI 0.8 to 0.99; RD -0.04, 95% CI -0.08 to 0.00; 3 studies, 2150 infants; moderate certainty evidence); and death or BPD (RR 0.89, 95% CI 0.81 to 0.97; RD -0.05, 95% CI -0.09 to 0.01; 3 studies, 2358 infants; moderate certainty evidence). There was also probably a reduction in the need for mechanical ventilation (failed treatment) (RR 0.49, 95% CI 0.45 to 0.54; RD -0.50, 95% CI -0.54 to -0.45; 2 studies, 1042 infants; moderate certainty evidence). There was probably a reduction in the incidence of death (RR 0.82, 95% CI 0.66 to 1.03; 3 studies, 2358 infants; moderate certainty evidence); pulmonary air leak (pneumothorax) (RR 1.24, 95% CI 0.91 to 1.69; 3 studies, 2357 infants; low certainty evidence); and IVH Grade 3 or 4 (RR 1.09, 95% CI 0.86 to 1.39; 3 studies, 2301 infants; moderate certainty evidence). One study in this comparison reported that there was probably little or no difference between the groups in the incidence of neurodevelopmental impairment at 18 to 22 months (RR 0.91, 95% CI 0.62 to 1.32; 976 infants; moderate certainty evidence). Prophylactic CPAP compared with very early CPAP There was one study in this comparison. We are very uncertain whether there is any difference in the incidence of BPD (RR 0.5, 95% CI 0.05 to 5.27; very low certainty evidence). The combined outcome of death and BPD was not reported, and failed treatment was reported but without data. There may have been little to no effect on death (RR 0.75, 95% CI 0.29 to1.94; 1 study, 72 infants; very low certainty evidence). Intraventricular haemorrhage Grade 3 or 4 and neurodevelopmental outcomes were not reported in this study. Pulmonary air leak (pneumothorax) was reported in this study, but there were no events in either group., Authors' Conclusions: For preterm and very preterm infants, there is insufficient evidence to evaluate prophylactic CPAP compared to oxygen therapy and other supportive care. When compared to mechanical ventilation, prophylactic nasal CPAP in very preterm infants reduces the incidence of BPD, the combined outcome of death and BPD, and mechanical ventilation. There is probably no difference in neurodevelopmental impairment at 18 to 22 months of age. When prophylactic CPAP is compared to early CPAP, we are very uncertain about whether there is any difference between prophylactic and very early CPAP. There is no information about the effect of prophylactic or very early CPAP in late preterm infants. There is one study awaiting classification., (Copyright © 2021 The Cochrane Collaboration. Published by John Wiley & Sons, Ltd.)